Practical guide
The rains arrive in the west, the Gulf stays mostly dry, and prices fall.
May is a shoulder month, and a good one if you choose the right coast. The southwest monsoon reaches the Andaman coast and Koh Chang, so Phuket and Krabi get regular storms and rougher seas, and the Similan Islands close on 16 May. The Gulf islands (Koh Samui, Koh Phangan, Koh Tao) and Hua Hin stay mostly dry. Bangkok and the north get their first heavy storms, which clear the burning-season haze. Prices drop sharply from the high season, often by 30–50%.
Averages for eight weather stations, one for each part of the country. Tap a region in the table to jump to it, or switch to °F and inches.
| Region | High | Low | Rain | Rain days | Sea |
|---|---|---|---|---|---|
| Bangkok | 35°C | 27°C | 217 mm | 12 | – |
| Chiang Mai | 35°C | 24°C | 168 mm | 12 | – |
| Phuket | 33°C | 26°C | 237 mm | 16 | 30°C |
| Koh Samui | 33°C | 26°C | 132 mm | 11 | 30°C |
| Pattaya | 33°C | 27°C | 121 mm | 9 | 30°C |
| Hua Hin | 34°C | 26°C | 96 mm | 8 | – |
| Koh Chang | 33°C | 25°C | 420 mm | 19 | 31°C |
| Isan | 35°C | 25°C | 155 mm | 11 | – |
Central plains and the capital
Highs of 35°C and lows of 27°C, 217 mm of rain on about 12 days, 6.3 hours of sun a day.
Still very hot, with the first heavy storms of the rainy season, usually late in the day. The rain cools the evenings.
The north: Chiang Mai, Chiang Rai, Pai
Highs of 35°C and lows of 24°C, 168 mm of rain on about 12 days, 7 hours of sun a day.
The rains arrive and wash out the burning-season haze, and the hills start to turn green.
Andaman coast: Phuket, Krabi, Koh Lanta, Khao Lak
Highs of 33°C and lows of 26°C, 237 mm of rain on about 16 days, sea at 30°C.
The southwest monsoon arrives. Rain days jump, red flags go up on the west-coast beaches and the Similan Islands close on 16 May.
Gulf islands: Koh Samui, Koh Phangan, Koh Tao
Highs of 33°C and lows of 26°C, 132 mm of rain on about 11 days, sea at 30°C.
The hottest month on the Gulf islands and still mostly dry. Koh Samui, Koh Phangan and Koh Tao are the beach choice this month.
Upper Gulf: Pattaya, Koh Samet, Rayong
Highs of 33°C and lows of 27°C, 121 mm of rain on about 9 days, sea at 30°C.
Showers become more frequent, though Pattaya sits in a sheltered part of the Gulf and gets less rain than the Andaman side.
Western Gulf: Hua Hin, Cha-am, Pranburi
Highs of 34°C and lows of 26°C, 96 mm of rain on about 8 days, 6.3 hours of sun a day.
Hua Hin's hottest month, with light showers. One of the driest stretches of coast during the rainy season.
Eastern seaboard: Koh Chang, Koh Kood, Koh Mak
Highs of 33°C and lows of 25°C, 420 mm of rain on about 19 days, sea at 31°C.
The monsoon arrives on the Trat coast and the rain builds fast. The quiet season starts here.
Northeast: Khon Kaen, Udon Thani, Korat, Buriram, Ubon
Highs of 35°C and lows of 25°C, 155 mm of rain on about 11 days, 6.1 hours of sun a day.
The first storms of the rainy season, which farmers wait for to start planting rice.
Source WMO Climatological Standard Normals 1991–2020 (Thai Meteorological Department stations). Averages for 1991–2020, and rain days count days with at least 1 mm. Sea temperatures: Climates to Travel monthly sea-surface averages. Koh Chang uses the Trat station on the facing mainland and Isan uses Khon Kaen.
Arriving in Koh Samui
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Head east to the Gulf. Koh Samui, Koh Phangan, Koh Tao and Hua Hin are the dry options, Bangkok works between storms, and the north is greener and clearer than in March and April.
Koh Samui, Koh Phangan and Koh Tao get their rainy season later in the year, from October to December, so May is still their good season, at lower prices than winter.
May has a royal holiday, a Buddhist holy day and the northeast's rocket festivals.
A public holiday marking King Vajiralongkorn's coronation.
Bun Bang Fai, the rocket festival, is held in towns across Isan to ask for rain before planting. The best known is in Yasothon, usually over a weekend in mid-May, with home-made rockets and processions.
The most important Buddhist holy day, marking the Buddha's birth, enlightenment and death, and a public holiday. Temples hold candlelit processions in the evening, and shops, convenience stores and ordinary restaurants stop selling alcohol for the day.
Moved a day to avoid Visakha Bucha. Haad Rin, Koh Phangan.
Low season starts, and hotel prices drop by 30–50% from the winter peak, more on the Andaman coast. You can usually book a few days ahead.
Storms are usually short but heavy, mostly in the afternoon or evening.
Still very hot and sunny between storms.
Things that dry overnight after an afternoon downpour.
Seas can be choppy and spray is likely on any boat trip.
Common questions about thailand in may.
Other months, and the whole year at a glance
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Written by
Mac Kiley
I lived in Bangkok for four years and traveled the country from there. The guides are my own opinions, written the way I'd explain them to a friend planning a trip.
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